Rare earths and other scarce metals – technologically vital but usually thrown away

A report of the RSC Environmental Chemistry Group’s Distinguished Guest Lecture and Symposium held on 20 March 2013 at Burlington House, London.

The Symposium was organised by ECG Committee Member Dr Stuart Wagland and chaired by Dr William Bloss (Chair of the RSC Environmental Chemistry Group). There were sixty attendees. The ECG Committee acknowledges support provided by the RSC Environment, Sustainability and Energy Division (ESED), the Chartered Institution of Wastes Management (CIWM) and the Chartered Institution of Water and Environmental Management (CIWEM).

The Symposium was opened by Professor Andrea Sella (University College London) with a talk on “Terra Rara – The Unknown Elemental Sea”, a survey of the origins, uses and chemical nature of the rare earth elements (REEs: scandium, yttrium, and the fifteen lanthanides). He began by emphasising that problems of sourcing REEs were problems of access not abundance. The similar sizes of REE ions means that their separation and purification are difficult; one calculation suggested that with classical nitric acid digestion methods, isolation of a rare earth from a mineral substrate could require some forty thousand recrystallisations. This theme of separation and purification has dominated REE extraction and use ever since Carl Auer von Welsbach used lanthanum and ytrrium oxides in gas mantles in 1886 and in 1903 patented the use of cerium in the ‘ferrocerium’ flints still in use today. Glassblowing and other technologies created more demand. As further uses emerged, a market for REEs developed and attention shifted to better methods for their isolation.

The first of these is described in a series of papers by Frank Spedding and colleagues in the Journal of the American Chemical Society starting in 1947. Their research championed the use of cation exchange resins to purify REEs from the fission products of nuclear reactions. A second change in methodology was introduced following work at Oak Ridge National Laboratory in the 1950s, when resin processes were replaced by more profitable continuous solvent extraction. However, the new techniques had downsides: nitric acid waste, releases of dust concentrate together with hydrofluoric acid, sulfur dioxide, and sulfuric acid, and the production of large amounts of radioactive residues were consequences of the continuous process. This created a concern about the environmental impacts of REE exploitation that continues to this day.

Over the last decade, increasing global demand for REEs means that geopolitical issues are increasing in importance and the exact nature of the developed world’s future need for REEs and the threats involved in sustaining supply have become salient. The strategic availability of REEs was covered by David Merriman (Roskill Information Services) in his talk on “A Review of Global Supply of Rare Earths”. He described how REEs occurred geologically as a consequence of hydrothermal deposition by igneous intrusions and could also be found in sand deposits and in low-cost clays. Before the 1990, the main supplier was Molycorp’s Mountain Pass mine in California, but by 2005, China had become responsible for 96% of global rare earth supply. This virtual monopoly did not go unnoticed, and in 2012 there were 200 global exploration projects seeking diversified sources of REEs in Angola, Argentina, Australia, Vietnam, Greenland and Tanzania. China’s domination of global REE trading is projected to decrease to 74% in 2015 and 61% in 2018, although China will still dominate the market for heavy REEs. Although growth in production by the rest of the world (mainly US and Australia) is expected, China will continue to dominate until beyond 2018. Urban mining (recycling) will not be a significant source of REEs until large-scale collection is implemented.

REEs are clearly causing a considerable global challenge. One approach to this challenge is to search for substitutes for REEs, as described by Dr Mike Pitts (Sustainability Manager, Technology Strategy Board) in his talk on “Chemistry Innovation in Resource Efficiency”. He referred to REEs as ‘Endangered Elements’ and argued that future (2050) demand will be insupportable unless design and manufacturing becomes focused on extending the life of manufactured goods and designing-in the capacity for goods to be remanufactured and easily recycled.

Adrian Chapman (Oakdene Hollins) spoke about “Materials’ Criticality – Mitigation Options and Impacts” in the context of the EU’s Strategic Energy Technology Plan, which has classified REEs as critical raw materials. The latter are a group that includes tin, platinum, graphite, fluorspar, magnesium, gallium, and beryllium. A material’s ‘criticality’ is obtained by associating risk with economic importance and the speaker made the point that ‘critical’ does not mean crisis and that ‘criticality’ is not linked to geological scarcity; most critical raw materials are abundant but difficult to win. An evaluation of environmental risk is one of the criteria used when a material’s criticality is assessed.

Once critical raw materials have been identified there are a variety of approaches possible, including better data collection and dissemination (to improve evaluations of the supply situation); procurement and stockpiling (Japan and the US have adopted this approach); trade and international co-operation (trade is currently dominated by China and this is an inherently unstable situation); design and innovation (substitution); and resource efficiency strategies (better extraction, more recycling, greater impact mitigation and more designed-in capacity for re-use).

As seen previously, when REEs were being purified, chemistry had a role in helping to improve resource use efficiency; increasing this efficiency will make access to lower grade ores financially viable, thereby reducing supply risk. Chemistry also has a role in minimising environmental damage by developing new technologies and pollution mitigation schemes and, since many critical raw materials are by-products of base metals, chemistry can also help to improve base-metal production methods to facilitate access to REE by-products. The speaker suggested that the REE content of manufactured goods could be reduced if the introduction of new materials and new products was accelerated. Due to the technical challenges of reclaiming REEs from waste units (e.g. mobile phones), where they are present in very small quantities, recycling levels are low and recycling has not alleviated the problems of demand.

Professor Thomas Graedel (Yale University) encompassed many of the symposium’s themes in his Distinguished Guest Lecture “Rare Earths and Other Scarce Metals: Technologically Vital but Usually Thrown Away”. He introduced the concept of Industrial Ecology (IE: the study of material and energy flows through industrial systems) and then illustrated how model systems based on IE can be used to produce whole life cycle analyses of REE usage from ore extraction to disposal, from producers through manufacturers to receivers/users. He made the point that energy costs for extraction, purification, and fabrication of REE containing goods are so high that using once and then throwing away should not be an option. Dissipative uses (such as brake lining manufacture) should also be restrained.

Like the other speakers, Professor Graedel also addressed the ‘Challenge of Companionability’: the occurrence of REEs in association with large volume metals such as lead, zinc and iron. For instance, if construction decreases, less iron is used, demand for zinc as a galvaniser decreases, less zinc is mined, and less REEs are extracted as a by-product; REE sustainability is thus intimately linked to the demand for other metals that are quite unlike them in terms of properties and use.

In a manner analogous to the EU’s critical raw material approach but using a new methodology, the Yale Criticality Project accommodates REE risk factors in a single model of three complementary dimensions, namely supply risk, vulnerability to supply restriction, and environmental implications for human health and ecosystems. Supply risk contains terms to accommodate geology, regulatory threats, political stability, availability of investment etc., while vulnerability to supply restriction includes terms for the availability of substitute materials and/or different sources of REEs and for the effects of external economic impacts on the REE market by events such as those the EU is experiencing currently. Classifying risks into these categories and then assessing all risks to give accumulative scores for each category allows a representation of three composite risk element to be displayed for all REEs at a locus in a three-dimensional criticality space; uncertainty is evaluated using propagated errors from each of the terms contributing to the separate complementary dimensions and represented by a cloud in criticality space.

Professor Graedel closed by summarising his lecture in four main points: Metals occur in geological groups and this strongly influences availability; scarce metal companionability decouples price from production; many REEs are used once and then lost, often by design; and life cycle quantification presents the opportunities that are available to help change our ways. The meeting closed at 17.15 after questions.

(Part Five of Periodic Tales – The Curious Lives of the Elements, by Hugh Aldersey-Williams, Penguin Books Ltd, 2012, discusses the early history of REEs under headings such as Swedish Rock, Auerlicht, and Ytterby Gruva. I recommend it.)